Link of Manual of 'pintos'

http://www.scs.stanford.edu/10wi-cs140/pintos/pintos.html#SEC_Top

this is manual of "pintos Operating System"

Process Concept

Process in Memory

Process Concept

• An operating system executes a variety of programs:
• Jobs for batch system
• User program/ tasks for time-sharing system
• Textbook  uses the terms "job" and "process" almost interchangeably
• Process - a program in execution; process execution must progress in sequential fashion
• A process includes:
• program counter
• stack
• data section

Process State

• new : The process is being created
• running : Instructions are being executed
• waiting : The process is waiting for some event to occur
• ready : The process is waiting to be assigned to a process
• terminated : The process has finished execution

Diagram of Process State

참고  : Operating System Concepts by WILEY

Buffering & Spooling

Buffering

  Buffering은 I/O channel을 통하여 data가 buffer에 저장된 후,CPU가 buffer에 접근하여

연산을 수행하도록 한다. CPU가 buffer를 접근하는 동안 I/O channel을 통하여 data를 입력하는

것은 불가능하지만 CPU가 연산을 수행하는 동안에는 입력하는 것이 가능하다.

  따라서, buffer가 하나일 경우에는 CPU가 buffer에 접근하는 동안 I/O device는 idle 상태에 

있게 된다. 그러나 buffer를 두 개 사용하는 double buffering에서는 CPU가 하나의 버퍼에 접근하는

동안 다른 버퍼는 다음 data를 계속 입력받음으로써 CPU의 동작과 I/O device의 동작을 동시에

수행할 수 있게된다. circular buffering은 이러한 개념을 확장하여 세 개이상의 buffer를 사용한다.

출력도 이와 유사한 buffering을 할 수 있다.

Spooling (Simultaneous Peripheral Operation On-line )

   buffering은 I/O device마다 buffer를 두지만 spooling은 disk를 하나의 매우 큰 buffer처럼 사용하며

disk를 통하여 I/O를 수행한다.

Comparison

   buffering과 spooling은 모두 I/O device와 CPU간의 속도 차이를 줄여 CPU 이용률을 개선하기 위한

방법이다. buffering은 단지 하나의 작업의 I/O와 CPU 연산을 동시 수행할 수 있지만 spooling은 여러 작업들간의 I/O와 CPU 연산을 동시에 수행할 수 있다. 따라서 spooling은 buffering에 비하여 system 성능에 직접적인 향상 효과를 일으킬 수 있다.

[출처] [ 운영체제 ] Buffering 과 Spooling|작성자 침해사고대응팀장

Operating-System Structure

Operating-System Structure

1. Simple Structure

• MS-DOS - Written to provide the most functionality in the least space

• Not divided into modules
• Although MS-DOS has some structure, its interfaces and levels of functionality are not well separated

2. Layered Approach

• The operating system is divided into a number of layers (levels), each built on top of lower layers
• The bottom layer (layer 0) is the hardware, the highest (layer N) is the user interface
• With modularity, layers are selected such that each uses functions (operations) and services of only lower-level layers

• #UNIX - limited by hardware functionality, the original UNIX operating system had limited structuring. The UNIX OS consists of two separable parts

• The kernel


• Consists of everything below the system-call interface and above the physical hardware
• Provides the file system, CPU scheduling, memory management, and other operating-system functions; a large number of functions for one level

UNIX System Structure

3. Microkernel System Structure

• Moves as much from the kernel into "user" space
• Communication takes place between user modules using message passing
• Benefits:
• Easier to extend a mocrokernel
• Easier to port the operating system to new architectures
• More reliable (less code is running in kernel mode)
• More secure
• Detriments:
• Performance overhead of user space to kernel space communication

Mac OS X Structure

Mac OS X is mixed structure (with Mach Microkernel and BSD kernel and kernel extension)

4. Modules

Solaris Modular Approach

• Most modern operating systems implement kernel modules
• Uses object-oriented approach
• Each core component is separate
• Each talks to the others over known interfaces
• Each is loadable as needed within the kernel
• Overall, similar to layers but with more flexible

Virtual Machines

Virtual Machines

• A virtual machine takes the layered approach to its logical conclusion. It treats hardware and the operating system kernel as though they were all hardware
• A virtual machine provides an interface identical to the underlying bare hardware
• The operating system creates the illusion of multiple processes, each executing on its own processor with its own (virtual) memory
• The resources of the physical computer are shared to create the virtual machines



The Java Virtual Machine

• CPU scheduling can create the appearance that users have their own processor
• Spooling and a file system can provide virtual card readers and virtual line printers
• A normal user time-sharing terminal serves as the virtual machine operator's console
• The virtual-machine concept provides complete protection of system resources since each virtual machine is isolated from all other virtual machines. This isolation, however, permits no direct sharing of resources
• A virtual-machine system is a perfect vehicle for operating-systems research and development. System development is done on the virtual machine, instead of on a physical machine and so does not disrupt normal system operation
• The virtual machine concept is difficult to implement due to the effort required to provide an exact duplicate to the underlying machine

VMware Architecture

참고  : Operating System Concepts by WILEY

Operating System Services and User Interface

Operating System Services

1. One set of operating - system services provides functions that are helpful to the user
• User interface : CLI (Command-Line Interface), GUI (Graphics User Interface), BPS (Batch Process System)
• Program execution
• I/O operations
• File-system manipulation
• Communications
• Error detection
2. Another set of OS functions exists for ensuring the efficient operation of the system itself via resource sharing
• Resource allocation
• Accounting (to record using time)
• Protection and Security

User Operating System Interface

1. CLI
• Sometimes implemented in kernel, sometimes by systems program
• Sometimes multiple flavors implemented - shells
• Primarily fetches a command from user and executes it
2. GUI
• User-friendly desktop metaphor interface
• Many systems now include both CLI and GUI interfaces
• Microsoft Windows is GUI with CLI "command"shell
• Apple Mac OS X as "Aqua" GUI interface with UNIX kernel underneath and shells available
• Solaris is CLI with GUI interfaces (Java Desktop, KDE)

참고  : Operating System Concepts by WILEY

System Call

API - System Call - OS Relationship

System Calls

• Programming interface to the services provided by the OS
• Typically written in a high-level language (C or C++)
• Mostly accessed by programs via a high-level Application Program Interface(API) rather than direct system call use
• Three most common APIs are Win32 API for Windows, POSIX API for PISIX-based systems (including virtually all versions of UNIX, Linux, and Mac OS X), and Java API for the Java virtual machine (JVM)

System Call Implementation

• Typically, a number associated with each system call
• System-call interface maintains a table indexed according to these numbers
• The system call interface invokes intended system call in OS kernel and returns status of the system call and any return values
• The caller need know nothing about how the system call is implemented
• Just needs to obey API and understand what OS will do as a result call
• Most details of OS interface hidden from programmer by API
• Managed by run-time support library (set of functions built into libraries included with compiler)

Standard C Library Example

C program invoking printf() library call, which calls write() system call

참고  : Operating System Concepts by WILEY 

Operating System Structure & Activities

Operating System Structure

• Multiprogramming - One job selected and run via job scheduling
• Timesharing(multitasking) - Timesharing is logical extension in which CPU switches jobs so frequently that users can interact with each jab while it is running, creating interactive computing

Operating-System Operations

• Interrupt driven by hardware
• Software error or request creates exception or trap
• Other process problems include infinite loop, processes modifying each other or the operating system

1. Dual-mode - Dual-mode operation allows OS to protect itself and other system components
• User mode and Kernel mode
• Mode bit povided by hardware
• user mode : 1 (included typical codes) 
• kernel mode : 0 (included I/O codes)
2. Timer - To prevent infinite loop/process hogging resources
• Set interrupt after specific period
• Operating system decrements counter
• When counter zero generate an interrupt
• Set up before scheduling process to regain control or terminate program that exceeds allotted time

Operating-System Activities

1. Process Management Activities
• Creating and deleting both user and system processes
• Suspending and resuming processes
• Providing mechanisms for process communication
• Providing mechanisms for deadlock handling
2. Memory Management Activities
• Keeping track of which parts of memory are currently being used and by whom
• Deciding which processes(or parts thereof) and data to move into and out of memory
• Allocating and deallocating memory space as needed
3. Storage Management Activities
• Creating and deleting files and directories
• Primitives to manipulate files and dirs
• Mapping files onto secondary storage
• Backup files onto stable storage media
4. Mass-Storage Management Activities
• Free-space management
• Storage allocation
• Disk scheduling
• Caching
• Important principle, performed at many levels in a computer(in hardware, operating system, software)
• Information in use copied from slower to faster storage temporarily
• Faster storage (cache) checked first to determine if information is there
• If it is, information used directly from the cache (fast)
• If not, data copied to cache and used there
• Cache smaller than storage being cached
• Cache management important design problem
• Cache size and replacement policy
• I/O Subsystem
• One purpose of OS is to hide peculiarities of hardware devices from the user
• I/O subsystem responsible for
• - Memory management of I/O including buffering, caching, spooling
• #buffering is storing data temporarily while it is being transferred
• #spooling is the overlapping of output of one job with input of other jobs
• - General device-driver interface
• - Drivers for specific hardware devices

참고  : Operating System Concepts by WILEY

How a Modern Computer System Works

How a Modern Computer System Works

Computer-System Operation

• I/O devices and the CPU can execute concurrently
• Each device controller is in charge of a particular device type
• Each device controller has a local buffer
• CPU moves data from/to main memory to/from local buffers
• I/O is from the device to local buffer of controller
• Device controller informs CPU that it has finished its operation by causing an interrupt

Direct Memory Access Structure

• Used for high-speed I/O devices able to transmit information at close to memory speeds
• Device controller transfers blocks of data from buffer storage directly to main memory without CPU intervention
• Only one interrupt is generated per block, rather than the one interrupt per byte

참고  : Operating System Concepts by WILEY

Outline of Operating System

What is an Operating System?

• A program that acts as an intermediary between a  user of a computer and the computer hardware

Operating system goals

• Execute user programs and make solving user problems easier
• Make the computer system convenient to use
• Use the computer hardware in an efficient manner

Computer System Components

• Hardware
• CPU, memory, I/O devices
• Operating system - Controls and coordinates use of hardware among various applications and users
• Application programs
• Users
• People, machines, other computers

Operating System Definitions

• Resource allocator - manages and allocates resources
• Control program - controls the execution of user programs and operations of I/O devices
• Kernel - the one program running at all times

참고  : Operating System Concepts by WILEY